1. Field of the Invention
The invention relates to a device for actuating sealing jaws and for controlling their pressing-on time, especially for the sealing of folding tabs of a packaging blank in conjunction with a packaging machine.
2. Description of the Prior Art
Packaging machines are equipped with welding or sealing members, in particular heated sealing jaws, when articles are wrapped in sealable packaging material. During the production of the cigarette pack, its outer wrapping, consisting of thermally weldable film, is provided in the region of end faces with folding tabs overlapping one another. These are fixed in their closing position by sealing. To carry out the sealing operation, the (heated) sealing jaws are brought up against the faces of the packs to be sealed or up against the folding tabs for a limited period of time.
The sealing time, in particular the time during which the sealing jaws rest against the packs, has to be adhered to exactly in the light of the technological properties of the packaging material and with other circumstances being taken into account. It becomes more difficult to ensure exact, constant sealing times, at the same time with a predetermined pressure and a specific temperature of the sealing jaws, because the packs to be sealed can be transported at changing speeds within the packaging machine. This is because of necessary variations in the cycle time or cycle rate of the packaging machine. During operation, in principle at least three different performance ranges of the packaging machine can occur: normal speed corresponds to the predetermined output of the packaging machine, for example 400 cycles per minute in the production of cigarette packs. To carry out work on the packaging machine, for example in order to eliminate defective packs, etc., crawling speed is set, and under these conditions the packaging machine runs at a much reduced cycle rate, for example at 200 cycles per minute. Finally, packaging machines are equipped with a so-called overdrive which for a short time allows cycle rates above the normal speed.